Vehicles and wireless devices include an increasing variety and amount of communication capabilities and available services. These capabilities and services include global positioning system (GPS) receivers for determining a vehicle or wireless device position. GPS is one example of a global navigation satellite system (GNSS) system. A GNSS system includes a network of satellites that orbits the earth and provides location services to individuals and devices using receivers capable of receiving data provided by the satellites. GPS uses a constellation of between 24 and 32 satellites transmitting precise radio wave signals that allow a GPS receiver to determine a current location, a precise time, and a velocity. Presently, a large number of vehicles and wireless devices leave a factory with equipment—such as a GPS receiver—capable of receiving the precise radio wave signals and determining location. Among other capabilities, these vehicles and/or wireless devices are able to transmit location information to a call center or other central facility and communicate with the call center. As a result, someone using the vehicle or wireless device equipped to receive the precise radio wave signals sends data from the vehicle or wireless device that can facilitate a service provided by the call center.
However, the performance of any one of the satellites in the constellation can vary. For instance, GPS is designed to provide at least six satellites in view from any point on the earth's surface. Sometimes, even though six or more satellites are within a line of sight, the performance of one or more of these satellites degrades to the point that the satellite(s) cannot provide positional information. As a result, the location calculated by the GPS receiver or other equipment capable of receiving the precise radio wave signals suffers from error or may not be as accurate as desired.
Attempts have been made to reduce the magnitude and frequency of GPS errors using satellite based augmentation systems (SBAS). One example of an SBAS is the Wide Area Augmentation System (WAAS). The WAAS is an aircraft navigation aid that uses a network of ground-based reference stations to measure small variations in the satellite signals of GPS satellites. These measurements are then sent to master stations that generate corrections. The corrections are transmitted to a space-based segment of WAAS comprising WAAS satellites that communicate the corrections to WAAS-equipped GPS receivers. While WAAS helps reduce GPS error, several limitations exist. For instance, WAAS error correction is generally used by WAAS-equipped receivers that are more expensive than GPS receivers that are unable to use WAAS. In addition, non-SBAS-equipped GPS receivers can provide inaccurate data to the call center reducing the value of call center services.